Repeater for transmission lines



H. A. BARTON ET AL REPEATER FOR TRANSMISSION LINES Filed Jan. 27,

All.

HIM/11w A TTORNE Y July 20 1926.

MAM AAAAAM "In" Mun glllhllh nn 'WI 1 "I principle of the Events i thelatented July 20, W26.

RENEE A. BARTON, 033 NEW YORK, AND HARRY NYQUIST, OF ELMKURST, NEW YDRK,

ASSIGNGQRS TO AMERIGAN TELEPHONE AND TELEGRAPH COMPANY, A GORPORA- TION015' NEW YORK.

BEPEATER FOR TRANSMISSION LDQ'ES.

Application filed January 2?, ma. Serial 1%. e15,s7e.

this an object of our invention to im another ob'ect is to equalize theellect of lines of di erentlcngth on a repeater of the type whichrepeats hoth ways with a-single amplifyin glects of arinvention will:oecome apparent on con ation or a. limited number of specific examplesof practice in accordance with the invention whi are disclosed in thefol-lowing specie or: taken with the aceompa dra: it will be understoodthat the escription applies to these aaamp mention and that the cope-ortnveno is pointed out in zended Etererxdcg 3: element These and otherdbrawings, Figure 1 is a diagram of iission line embodying ourinvention. fig. .2 is a curve diagram that will referred to in exlaining the and Figs. 3. and .3 illustrate respectively different waysoi realizing the invention in connection with. over which both side andphantom circuits operated. I

Fl 1 represents a telephone transmission line intendedtor simultaneoustwo-way operation and compiising an interposed repeateroi the so-calledfill-type. This means that the repeater operates both ways but uses onlya single emplifymg element A for this purpose. The usual three-windinghynerd-transformer T 1s designed so that 1f the lines vextending eachway therefrom are equal 111 all respects, then an incoming Wave.

on eitherline will go in part to the input side of the amplifier A. Theamplified output will then go equally to the line both ways vfrom thetransformer and none of this output will get back to the input of theamplifier A, because of the absence of any potential drop across theinput terminals due to the'balanced output.

The impulses put upon the line from the p r sfit W 3 be tefl ted back isI also be increase some degree from the terminal stations E and W and ifthese are both far distant, any reflection is highly attenuated beforeit returns to the repeater. If either or both terminals are not fardistant the reflected waves may have considerable magnitude and willenter the input of the amplifier A.

In the case where one station W is near and the other station E isdistant it is ossible to improve the circuit bymeans W ich will ;bedescribed.

It might appear that to lengthen the line to ,station W by interposingartificial line would do more harm than goodbecause such interposedartificial line must attenuate the transmission either way between thetwo stations E and W. But in accordance with the principle of ourinvention, as we shall show,- there may be a positive advantage gainedby interposinga properly de signed artificial linebetween the repeaterand the nearer station W.

The network or artificial line N is interposed, as shown in F ig. 1. Letits equivalent in' standard miles. be represented by the character L.Since a wave going out from the repeater to-the station. W and reflectedback therefrom most traverse the network N twice, the attenuating ellecton that wave due to interposing the network N will be represented by 2L.But so far as transmission is'concerned from E to W Y or from W to E,the attenuating efiect of the network N is only L. v

If sufilcient gain is given bythe-amplify Eng element to overcome theattenuation of the reflected wave, singing or. sustained oscillationsare set up. Theelement A will be adjusted to give a gain which is lessthan the singing gain by a specific margin, e. g. 5 standard miles whichmust be allowed between singing and operating gain in order to securegood quality. sition of the network N the attenuation of the reflectedwaves has been. increased by 2L so that the ain in the amplifier A canby 2L and the margin of 5 miles betweensinging and o eratin gain isstill maintained. It should e note that. th fore o g s atement is t e, hfi fl By the interponumerical value this margin may have. The insertionof the net has-increased the transmission loss between E and W eitherway byL. However, it has made it possible to increase the gain of therepeater 2L which results in a net gain of L. I

'A. practical method for determining the propermagnitude of the networkN as measured in standard miles L will now be explained inconnection'with Fig. 2. By standard miles we refer to units ofattenuation of any apparatus interposed between a transmitting point anda receiving point, whose number L is-given by the formula Z=21.13 log Rwhere R- is the ratio .of received current when the apparatus is notinterposed to received current when it is interposed. Various values ofL are tried and the utmost repeater gain without singing is alsodetermined for each value of L. 'These values of L are laid off asabscissae. in Fig. 2 and the correspond ing values of gain forjtherepeater A are set Fig. 2.

But. since the gain in the repeater, as indicated by the curve G, isoffset to some extent by the loss L in the network N, a new curve markedG-L-is constructed by diminishing each ordinate of the curve by thecorresponding value for L. This curve G-L will have a distinct maximumIvaluc, as appears in F ig.- 2,-and the value of L at this maximum isthe appropriate value to be given to the network N.- Fig. 2.is drawn foran actual example of a 19 gauge medium heavy'loaded circuit containing a21-type repeater with 35 miles of line on one side and 10 miles on .theother side. It will be seen that there is a net improvement of 1.8standard miles by interposing 4.5 standard miles for the value of L inthe network N. I

The network N'must have the same characteristic impedance as the circuitin which it is interposed; this may be accomplished by design accordingto well understood principles.

Figs. 3, 4 and 5- show alternative ways in which the invention may bepracticed in connection with 'lines comprising side and phantomcircuits. The 21-type phantom group repeater is indicateddiagrammatically by the rectangle with the legend QI'I PG'R. In Fig. 3,a'network N is provided for each pair having in each conductor the tworesistances in series, each R/2. Bridged across between them is theshunt resistance 1'. R and 1' are given appropriatewalues in accordancewith well nown principles of design so that the network shall have.thesame characteristic impedance as the line and shall give the loss foundby the methodpreviously described. Then the mid-points of the two-shuntreup as ordinates, thus giving the curve G in' a complete independentsistances, each having the value 1', are con nected by a resistance psuch that Subject to this condition, the loss inserted in the phantomcircuit and th characteristic impedance presentedto it will beapproximately. correct.

It maybe necessary for the purpose of securing proper balance to usecondensers as shown in Fig. '3 by the character C to make thecharacteristic impedance of the inserted network more accurately equalto that of the line. $9

where the networks N are pilt in the local circuits determined by therepeatingcoils S, which are interposed inaccordance with the principleof phantom design. In this case, network N of proper design will beinterposed in the taps that goto complete the phantom circuit, as isshown in Fig. 1 5. An advantage of the arrangement in Fig. 5 is that itwill give less danger of cross-talk between the side circuits and thephantom circuit.

WVe claim:

-1. In combination, a 21-type repeater, two lines of different lengthextending thefefrom and .a network interposed in the line of shorterlength, said network having the same characteristic impedance as thelines, and an attenuation value such that the increase in the gain inthe repeater made possible by the interposed network will be more thanthe one-way transmission loss in the 195 network. v

2. The method of increasing the gain at which a 21-type repeater betweentwo lines of different length maybe operated, which consists in causingthe unbalance waves on the side of the shorter line to traverse aninterposed network twice of the same characteristic impedance as theline while the effective transmission will traverseit but once.

3. The method of determining the optimum attenuation to be introduced inthe shorter side of a transmission line with an interposed 21-typerepeater, which consists in plotting against said attenuation themaximum repeater gain diminished by said attenuation thus givingthedesired attenuatilon corresponding to the maximum. on the p ot. 4. Incombination, a transmission system comprising two sides and a phantomwith an lnterposed Pal-type phantom oup' repeater, networks in each sidemaking it its possible to im rovetransmission on each side with thesenetworks constituting means further to improve transmission on thephantom circuit.

5. In combination, a transmission systern comprising two sides and aphantom with m interposed 2l-typo phantom group repeater, aiidappropriate networks to make it possible "c-o improve transmission oneach side and on the phantom.

' In testimony whereof, we have signod our no names to thisspecification this 25th day of

